A 60-year-old hypertensive man started on enalapril develops recurrent episodes of lip and tongue swelling without urticaria or pruritus. Laboratory testing excludes C1 esterase inhibitor deficiency. The swelling results from accumulation of which inflammatory mediator normally degraded by the inhibited enzyme?

• A Substance P
• B Thromboxane A2
• C Leukotriene D4
• D Bradykinin ✓

Explanation

Angiotensin-converting enzyme is identical to kininase II, the enzyme that degrades bradykinin. ACE inhibition therefore raises kinin levels, and excess bradykinin increases venular permeability, producing angioedema of lips, tongue and airway. Hereditary angioedema from C1 inhibitor deficiency is excluded by testing. Leukotriene B4 drives bronchoconstriction in asthma, substance P mediates neurogenic pain and vasodilation, and thromboxane A2 aggregates platelets; none accumulates because of ACE inhibition.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.